Been looking at the new test helpers such as `runB...

# coroutines

[Marcelo Hernandez]

Been looking at the new test helpers such as runBlockingTest, TestCoroutineDispatcher, TestCoroutineScope, etc. They look promising, however I haven't been able to figure out a way to stub a dependency's suspend function using mockito-kotlin such that it suspends indefinitely. The goal is to test scenarios within my Android ViewModel where onCleared() is called before a suspend function returns a result. Basically something like:

private fun givenStatusNeverReceived() = runBlocking {
    // loadStatus() is a suspend function
    given(repository.loadStatus()).willAnswer {
        // suspend indefinitely
    }
}

[louiscad]

Use MockK, it supports coroutines

[Marcelo Hernandez]

Been meaning to explore MockK for some time. Our entire codebase has been using mockito-kotlin with a heavy focus on the BDDMockito APIs. I was hoping to maintain consistency moving forward, however with the recent introduction of coroutines in our codebase (we've been using RxJava heavily), it looks like mockito-kotlin is starting to show its limitations.

[louiscad]

I'd recommend to just try it at first. Also, I think you can have them side by side.

[Marcelo Hernandez]

Played around with MockK for a bit and it took some getting used to. I like how strict it is by default though. However, I do miss the style of BDDMockito. But MockK's coEvery, coAnswer, etc. APIs make it quite easy to mock/stub suspend functions.

[Marcelo Hernandez]

After playing around with it, I then got a few more ideas with mockito-kotlin and got something working, but it looks rather ugly IMO. Basically it's something like:

private val deferredStatus = CompletableDeferred<Status>()

...

private fun TestCoroutineScope.whileAwaitingStatus() {
    given(repository.loadStatus()).willAnswer {
        var result: Status? = null
        runBlockingTest {
            result = deferredStatus.await()
        }
        return result!!
    }
}

However, even if you choose to not set a value for the CompletableDeferred, you have to make sure to call cancel() on it otherwise runBlockingTest throws an exception indicating that there was still an active Job running.